var isSameTree = function(p, q) {
    if(p==null&&q==null){
        return true
    }
    if(p=null||q==null){
        return false
    }
    if(p.val!==p.val){
        return false
    }
    return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right)
}